This invention relates generally to a system and method for enhancing hearing in patients suffering from sensorineural hearing deficiencies and more particularly to a system including an electrically driven speaker implanted adjacent the middle ear cavity.
The prior art is replete with descriptions of various devices and techniques for enhancing hearing in patients suffering from sensorineural hearing deficiencies.
As an example, U.S. Pat. No. 5,913,815 contains an extensive description of the background of hearing aids and cites a multiplicity of prior patents and publications. For example, the ""815 patent discusses that xe2x80x9cThe vibratory structures of the ear include the tympanic membrane, ossicles (malleus, incus, and stapes), oval window, round window, and cochlea. Each of the vibratory structures of the ear vibrates to some degree when a person with normal hearing hears sound waves. However, hearing loss in a person may be evidenced by one or more vibratory structures vibrating less than normal or not at all.xe2x80x9d
The ""815 patent also mentions that xe2x80x9cVarious types of hearing aids have been developed to restore or improve hearing for the hearing impaired. With conventional hearing aids, sound is detected by a microphone, amplified using amplification circuitry, and transmitted in the form of acoustical energy by a speaker or another type of transducer into the middle ear by way of the tympanic membrane. Often the acoustical energy delivered by the speaker is detected by the microphone, causing a high-pitched feedback whistle. Moreover, the amplified sound produced by conventional hearing aids normally includes a significant amount of distortion.xe2x80x9d
In order to mitigate the aforementioned and other shortcomings of earlier devices and techniques, various efforts have been directed toward surgically implanting devices which produce vibrations by physical contact and before conduction.
The present invention is directed to a system which uses an electrically driven sound transducer, i.e., a speaker, implanted in the middle ear cavity. More particularly, in accordance with the invention, the speaker is implanted in the middle ear cavity inward of the tympanic membrane and oriented to direct sound energy toward the ossicles and thus, via the oval window, actuate the perilymph in the cochlea. In an alternative arrangement, the speaker functions to actuate the cochlea via sound injected into the round window.
Many prior art middle ear hearing aid devices rely on an actuator to physically vibrate one of the ear""s components, typically one of the three ear bones (ossicles) or one of the cochlea membranes. Indeed, some devices require penetration of the cochlea. This level of invasiveness presents a risk of aggravating, rather than mitigating, hearing impairment. The present invention considerably reduces the risk by relying on sound energy, rather than physical contact.
In accordance with the invention, a microphone is supported and/or implanted adjacent to the ear canal sufficiently isolated from the implanted speaker. The microphone is configured to respond to sound energy to generate an electric signal which drives the implanted speaker which is preferably contained in a hermetically sealed housing fixed to bony material adjacent to the middle ear cavity.
In accordance with a preferred system embodiment, the microphone comprises a component of an integrated microphone module including an analog-to-digital converter, sound processing circuitry, and encoding/modulation transmitter circuitry, all contained in a hermetically sealed housing. The housing includes a battery, preferably a lithium ion battery, which can be charged from an external source, as by an alternating magnetic field source.
In accordance with a preferred embodiment, the speaker comprises a component of an integrated speaker module including demodulation/decoding receiver circuitry, processing circuitry, and a digital-to-analog converter, all contained in a hermetically sealed housing. The speaker module housing contains a battery similar to that contained in the microphone module.
In accordance with a preferred system embodiment, sound insulation is preferably provided to direct sound energy primarily to the ossicles and middle ear oval window and away from the microphone. In order to minimize signal cancellation which could occur by in-phase sound energy also entering the round window, it is preferable to seal the round window. This sealing can take the form of a passive sound insulator or an active device (e.g., a second speaker) which produces the same signal but out of phase.
In an alternative preferred embodiment, the speaker is mounted close to the round window and insulated to minimize sound transmission to the microphone and the oval window.
In accordance with a further aspect of a preferred embodiment, a speaker placed in one ear can be driven by a microphone placed in the other ear. This arrangement reduces feedback.